The present invention relates to an assembly comprising a first cam carrier and at least one further cam carrier for a securement device for an adjustable steering column for a motor vehicle. Each cam carrier includes at least one cam, and the cam carriers are disposed opposite to one another such that they are rotatable against one another about a rotational axis. Upon the first cam carrier being rotated out of position against the further cam carrier along a turning angle about the rotational axis, the cam of the first cam carrier comes to rest glidingly on the cam of the further cam carrier along a contact path.
Generic assemblies are employed in securement devices or clamping devices for adjustable steering columns for motor vehicles. By means of a lever, most often manually operatable, the cam carriers can be rotated out of position against one another. In a first position, the securement device is subsequently in an open position in which the steering shaft, and therewith the steering wheel attached on the steering column, can be adjusted in the height and/or length position in order to adapt the position of the steering wheel to the position of the particular driver. Within the prior art, different cam carriers are known in which the cams are formed out differently, thus have a cam contour differing from one another. There is frequently also reference made to a cam or cam carrier and a cam follower cooperating therewith. However, this is merely a linguistic convention. In the final analysis the cam carriers and cam followers involve each a cam carrier with corresponding cams.
A general problem in the preparation or outforming of the cams consists in providing on a shortest possible displacement path or turning angle the largest possible pressing force for arresting the securement device in its closed position. The manual force, which is required for the actuation of the lever of the securement device, is simultaneously to be kept at the lowest possible level and convey the impression of a comfortable and easy actuation. Furthermore, the wear on the cam is to be kept as low as feasible.
For an improvement of the operatability of the cam surface, EP 1 180 466 proposes implementing the cam surface with a multiplicity of sloping ramps whose slopes differ in order to attain as uniform as possible a transition of the manual force as a function of the turning angle and therewith of the clamping force. Within prior art, moreover, there are known general curveform ramps, thus, for example, as disclosed in JP 2003-231470A. In JP 2005-231545A a cam ramp is also described.
According to JP 2006-131211A the specific required clamping force is to be represented with an optimized manual force progression. For this purpose JP 2006-131211A proposes implementing the contact faces between cams and cam follower, which, in the closed state of the clamping system, are in engagement with one another, such that the clamping progression on the contact face is as uniform as possible along a line extending outwardly from the rotational center or the rotational axis of the cam carrier. For this purpose, the cam contact is initially closed starting from the radially outer end. According to this document, the elastic deformations in the cam are correspondingly larger than the thermal expansions of the structural parts anticipated during operation. Due to the elastic deformations anticipated from the outset and the only minor values of the superelevation, this technical solution makes high demands of the precision of the individual structural parts and therewith of the fabrication tolerances. Moreover, the durability of cam carrier and cams can only be attained with high expenditures since specific elastic deformations are provided in order to attain the uniform force progression.
All of the prior art listed above have in common that the manual force progression can only be optimized within narrow limits.